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Case 490 - Discussion

Uploaded: 2011-04-25, Updated: 2011-04-25



 Diagnosis: Pneumocystis Pneumonia


Pneumocystis Pneumonia

  • Intra-alveolar frothy infiltrates with a bubbly, vacuolated appearance;

  • Alveolar septa with pneumocyte hyperplasia and mild chronic inflammation;

  • Pneumocystis jiroveci:

    • Formerly carinii, belongs to fungi rather than protozoa;

    • 5-8 um, central dark dot, grooves and folds, partially collapsed cyst with helmet and crescent shapes, no budding;

    • GMS positive.

  • May show a wild range of histologic features: frothy exudates in the interstitium or alveolar spaces, necrotizing granuloma, diffuse alveolar damage, or minimal histologic damage.

Pulmonary Alveolar Proteinosis (PAP)

  • Intra-alveolar accumulation of lipid-rich, surfactant like material, due to increased surfactant production or impaired clearance;

  • Intra-alveolar accumulations of eosinophilic material, coarsely granular, large granules, sharply round empty spaces, cholesterol clefts;

  • No marked interstitial inflammatory infiltrates;

  • PAS positive, surfactant apoprotein posiitive.

  • EM: concentrically laminated myelin and lamellar bodies;

  • May be associated with nocardia infection.

Cytomegalovirus Pneumonia

  • Miliary pattern: multicentric lesions with alveolar exudates composed of fibrin and mixed inflammatory cells; central necrosis; classic CMV inclusions;

  • Diffuse interstitial pattern: mildly to fully developed damage; type II pneumocyte hyperplasia, CMV inclusions;

  • CMV antibody positive;

  • Differential diagnosis of inclusions:

    • CMV inclusion: enlarged nuclei, large eosinophilic to basophilic nuclear inclusions surrounded by a halo; frequent intracytoplasmic inclusions;

    • HSV inclusion: multinucleation, margination, molding; intranuclear eosinophilic inclusion, not intracytoplasmic;

    • RSV: multinucleation, eosinophilic intracytoplasmic inclusions with perinuclear arrangement, not intranuclear;

    • Adenovirus: smudge cells with basophilic inclusion that obscures the nuclear membrane; or eosinophilic inclusions surrounded by a clear halo that resemble CMV or HSV;

    • Measles: extremely large multinucleated giant cells with both nuclear and cytoplasmic inclusions, the intranuclear inclusions are eosinophic with a clear halo, the cytoplasmic inclusions are eosinophilic, granular in variable sizes.

Adenovirus Pneumonia

  • Necrotizing bronchitis and bronchiolitis;

  • Interstitial pneumonia with necrosis, hemorrhage, and diffuse alveolar damage;

  • Smudge cells: basophilic inclusion that obscures the nuclear membrane, may have halo.


  • PIP, 2008-A;

  • Non-Neoplastic Disorders of the Lower Respiratory Tract, series 4.